1. Field of the Invention
The present invention relates to a magnetic head for perpendicular magnetic recording that is used for writing data on a recording medium by using a perpendicular magnetic recording system and to a method of manufacturing such a magnetic head.
2. Description of the Related Art
The recording systems of magnetic read/write devices include a longitudinal magnetic recording system wherein signals are magnetized in the direction along the surface of the recording medium (the longitudinal direction) and a perpendicular magnetic recording system wherein signals are magnetized in the direction orthogonal to the surface of the recording medium. It is known that the perpendicular magnetic recording system is harder to be affected by thermal fluctuation of the recording medium and capable of implementing higher linear recording density, compared to the longitudinal magnetic recording system.
Magnetic heads for perpendicular magnetic recording typically used have a layered structure comprising a reproducing (read) head having a magnetoresistive element (that may be hereinafter called an MR element) for reading and a recording (write) head having an induction-type electromagnetic transducer for writing. The write head comprises magnetic poles that produce a magnetic field in the direction orthogonal to the surface of the recording medium.
For the perpendicular magnetic recording system it is an improvement in recording medium and an improvement in write head that mainly contributes to an improvement in recording density. It is a reduction in track width and an improvement in writing characteristics that is particularly required for the write head to achieve higher recording density. On the other hand, if the track width is reduced, the writing characteristics, such as an overwrite property that is a parameter indicating an overwriting capability, are reduced. It is therefore required to achieve better writing characteristics as the track width is reduced.
A magnetic head used for a magnetic disk drive such as a hard disk drive is typically provided in a slider. The slider has a medium facing surface that faces toward a recording medium. This medium facing surface has an air-inflow-side end and an air-outflow-side end. The slider slightly flies over the surface of the recording medium by means of the airflow that comes from the air-inflow-side end into the space between the medium facing surface and the recording medium. The magnetic head is typically disposed near the air-outflow-side end of the medium facing surface of the slider. In a magnetic disk drive the magnetic head is aligned through the use of a rotary actuator, for example. In this case, the magnetic head moves over the recording medium along a circular orbit centered on the center of rotation of the rotary actuator. In such a magnetic disk drive, a tilt called a skew of the magnetic head is created with respect to the tangent of the circular track, in accordance with the position of the magnetic head across the tracks.
In a magnetic disk drive of the perpendicular magnetic recording system that exhibits a better capability of writing on a recording medium than the longitudinal magnetic recording system, in particular, if the above-mentioned skew is created, problems arise, such as a phenomenon in which data stored on an adjacent track is erased when data is written on a specific track (that is hereinafter called adjacent track erasing) or unwanted writing is performed on adjacent two tracks. To achieve higher recording density, it is required to suppress adjacent track erasing. Unwanted writing on adjacent two tracks affects detection of servo signals for alignment of the magnetic head and the signal-to-noise ratio of a read signal.
A technique is known for preventing the problems resulting from the skew as described above, as disclosed in the Published U.S. Patent Application No. 2003/0151850 A1, the Published Unexamined Japanese Patent Application 2003-203311, and the U.S. Pat. No. 6,504,675 B1, for example. According to this technique, the end face of the pole located in the medium facing surface is made to have a shape of trapezoid in which the side located backward in the direction of travel of the recording medium (that is, the side located on the air-inflow-end side of the slider) is smaller than the other side.
As a magnetic head for perpendicular magnetic recording, a magnetic head comprising a magnetic pole and a shield is known, as disclosed in the U.S. Pat. No. 4,656,546, for example. In this magnetic head an end of the shield is located forward of an end of the pole along the direction of travel of the recording medium with a specific small space. Such a magnetic head will be hereinafter called a shield-type head. In the shield-type head the shield prevents a magnetic flux from reaching the recording medium, the flux being generated from the end of the pole and extending in directions except the direction orthogonal to the surface of the recording medium. The shield-type head achieves a further improvement in linear recording density.
The U.S. Pat. No. 4,672,493 discloses a magnetic head having a structure in which magnetic layers are provided forward and backward, respectively, in the direction of travel of the recording medium with respect to a middle magnetic layer to be the pole, and coils are disposed between the middle magnetic layer and the forward magnetic layer, and between the middle magnetic layer and the backward magnetic layer, respectively. This magnetic head is capable of increasing components orthogonal to the surface of the recording medium among components of the magnetic field generated from the medium-facing-surface-side end of the middle magnetic layer.
Reference is now made to FIG. 29 to describe a basic configuration of the shield-type head. FIG. 29 is a front view of a portion of the medium facing surface of an example of the shield-type head. The shield-type head comprises: a medium facing surface that faces toward a recording medium; a coil (not shown) for generating a field corresponding to data to be written on the medium; a pole layer 116 having an end located in the medium facing surface, allowing a magnetic flux corresponding to the field generated by the coil to pass and generating a write magnetic field for writing the data on the medium by means of the perpendicular magnetic recording system; a shield layer 120 having an end located in the medium facing surface and having a portion located away from the medium facing surface and coupled to the pole layer 116; and a gap layer 118 provided between the pole layer 116 and the shield layer 120. In this example the pole layer 116 is disposed on an insulating layer 114. An insulating layer 117 is provided around the pole layer 116. The pole layer 116 and the insulating layer 117 have flattened top surfaces on which the gap layer 118 is disposed. The shield layer 120 is further disposed on the gap layer 118.
The end of the pole layer 116 located in the medium facing surface has a shape of trapezoid in which the side closer to the gap layer 118 is longer than the other side.
Problems of the shield-type heads such as the one shown in FIG. 29 will now be described. In FIG. 29 the physical track width PTW is determined by the width of a portion of the end of the pole layer 116 located in the medium facing surface, the portion being in contact with the gap layer 118. However, a magnetic flux 121 starting from the pole layer 116 over the gap layer 118 and reaching the shield layer 120 extends wider than the physical track width PTW. Consequently, the effective track width ETW is greater than the physical track width PTW. For example, if the physical track width PTW is 0.12 micrometer (μm), the thickness of the pole layer 116 is 0.3 μm, and the thickness of the gap layer 118 is 50 nanometers (nm), the effective track width ETW is greater than the physical track width PTW by no less than 0.08 to 0.12 μm, according to conventional devices.
If the effective track width ETW is much greater than the physical track width PTW as described above, problems arises, such as adjacent track erasing and unwanted writing performed on adjacent two tracks. If the physical track width PTW is reduced to reduce the effective track width ETW, it is difficult to control the physical track width PTW and the overwrite property is reduced.